2,3-Diphosphoglycerate (2,3-DPG) is one of the important physiological effectors of hemoglobin in the human red blood cell. It binds more tightly to deoxyhemoglobin than to the oxy form, decreasing the oxygen affinity of hemoglobin. We are studying the regulation of the 2,3-DPG level in the red blood cell. At certain times, such as with blood transfusion (stored blood is low in 2,3-DPG) or to aid in accommodation to high attidude, it would be highly desirable to be able to increase the level of 2,3-DPG in the blood rapidly. On the other hand, in sickle cell anemia it might be beneficial to decrease the 2,3-DPG level, since the abnormally high 2,3-DPG level of such red cells tends to keep the hemoglobin in the deoxy form, which is the form that sickles. We are testing inhibitors and activators of diphosphoglycerate phosphatase as possible pharmacologic agents to regulate the level of 2,3-DPG in red cells. We are studying the enzymes involved in 2,3-DPG metabolism in the red cell: phosphoglycerate mutase (glycerate-3-P yields (reversibly) glycerate-2-P) and bisphosphoglycerate synthase which is the single enzyme that synthesizes and hydrolyzes 2,3-DPG in vivo. Each enzyme can be phosphorylated by 2,3-DPG on a unique histidine residue to form a functional phosphoenzyme. The three dimensional structure and complete amino acid sequence of yeast phosphoglycerate mutase are being determined in other laboratories. With that information and the results of our kinetic studies we hope to learn how these phosphoryl transfer reactions occur to gain further insights into the relationships between structure and function in enzymatic catalysis.